Doomtron appeared in 2001 TV series finale called Power Rangers Time Force. Doomtron is an evil giant robot created by Frax. It is also powered by Frax, who is able to board it and control Doomtron.
Doomtron's energy comes from a Trizirium crystal, which is kept inside Frax when he is wired to Doomtron's systems. Doomtron proves a hard robot to defeat, as he beats the Q-Rex Zord in battle and wreaks havoc across the city, opening large vortexes in the sky, until the Time Force Rangers join in the fight in the Time Force Megazord Jet Mode, which temporarily knocks Doomtron from the fight with Cyclone Defense. Doomtron quickly recovers and the Megazord battles it, holding it off long enough for Wes Collins to neutralize the Q-Rex's Trizirium Crystal power source. Wes then takes command of the Q-Rex and has the Q-Rex fire on Doomtron. The blast destroys Doomtron's crystal power source and Doomtron explodes, destroying Frax as well.